For preparing .alpha.-olefin polymers, there have been heretofore known processes for copolymerizing ethylene and .alpha.-olefin in the presence of a titanium catalyst composed of a titanium compound and an organoaluminum compound or a vanadium catalyst composed of a vanadium compound and an organoaluminum compound.
The ethylene/.alpha.-olefin copolymers obtained by using a titanium catalyst generally have a wide molecular-weight distribution and a wide composition distribution, and are deteriorated in transparency, anti-surface stickiness and mechanical and physical properties. On the other hand, the ethylene/.alpha.-olefin copolymers obtained by using a vanadium catalyst have a molecular-weight distribution and a composition distribution both narrower than those obtained using the titanium catalyst, and they are relatively improved in the transparency, anti-surface stickiness and mechanical and physical properties. However, those properties are still insufficient for various use applications requiring high properties. Hence, now required are catalysts capable of producing .alpha.-olefin polymers, particularly ethylene/.alpha.-olefin copolymers, much more improved in those properties.
There has recently been developed a new Ziegler type catalyst for olefin polymerization comprising a zirconium compound and an aluminoxane. For example, processes for the preparation of ethylene/.alpha.-olefin copolymers using this new Ziegler type catalyst have been proposed in Japanese Patent Provisional Publications, No. 58 (1983)-19309, No. 60 (1985)-35005, No. 60 (1985)-35006, No. 60 (1985)-35007, No. 60 (1985) 35008, etc.
The catalysts composed of a transition metal compound and an aluminoxane proposed in the prior art are excellent in polymerization activities, especially ethylene polymerization activities, as compared with catalysts having been known prior to the appearance of these catalysts which are composed of a transition metal compound and an organoaluminum compound. However, most of the catalysts are soluble in the reaction system, and in most cases the processes for the preparation are limited to a solution polymerization system. In addition, the catalysts have such a problem that, when the manufacture of a polymer having a high molecular weight is tried, the productivity of a polymer is lowered due to a marked increase in the viscosity of the polymer-containing solution.
On the other hand, polymerization of olefin has been tried in a suspension polymerization system or a gas phase polymerization system by using catalysts in which at least one of the transition metal compound component and the aluminoxane component described above is supported on a porous inorganic oxide carrier such as silica, alumina and silica-alumina.
For example, the aforementioned Japanese Patent Provisional Publications No. 60 (1985)-35006, No. 60 (1985)-35007 and No. 60(1985)-35008 disclose that there can be used catalysts in which a transition metal compound and an aluminoxane are supported on silica, alumina, silica-alumina, etc.
Further, the above publications and Japanese Patent Provisional Publications No. 61(1986)-130314 and No. 2(1990)-41303 disclose that a catalyst system in which a metallocene compound of a transition metal compound having, as a ligand, a pentadienyl group (e.g., cyclopentadienyl group), an alkyl group and/or a halogen atom is combined with aluminoxane has a high activity for olefin polymerization and can produce a polymer of excellent properties.
Furthermore, Japanese Patent Provisional Publications No. 60(1985)-106808 and No. 60(1985)-106809 disclose a process for the preparation of a composition composed of an ethylene polymer and a filler. This process comprises polymerizing ethylene or copolymerizing ethylene and .alpha.-olefin in the presence of an organoaluminum compound and a filler having an affinity for polyolefin, and a product prepared by pre-contacting a highly activated catalyst component containing a hydrocarbon-soluble titanium compound and/or a zirconium compound with a filler.
Japanese Patent Provisional Publication No. 61(1986)-31404 discloses a process for polymerizing ethylene or copolymerizing ethylene and .alpha.-olefin in the presence of a mixed catalyst composed of a transition metal compound and a product obtained by a reaction of trialkylaluminum and water in the presence of silicon dioxide or aluminum oxide.
Furthermore, Japanese Patent Provisional Publications No. 61(1986)-108610 and No. 61(1986)-296008 discloses a process for polymerizing olefin in the presence of a catalyst in which a transition metal compound such as metallocene and an aluminoxane are supported on a carrier such as an inorganic oxide.
However, in the case of polymerizing or copolymerizing olefin in a suspension or gas phase using such a solid catalyst component supported on a carrier as described in the above-mentioned publications, the polymerization activities are markedly lower as compared with the above-described solution polymerization.
In "Journal of Organometallic Chemistry", 363 (1989), C12 to C14 are disclosed Cp.sub.2 Zr (CF.sub.3 SO.sub.3).sub.2 (THF) and [Cp.sub.2 Zr(CF.sub.3 SO.sub.3) (bipy)].sup.+ CF.sub.3 SO3.sup.-, but these two compounds are lower in olefin polymerization activities as compared with the above-mentioned cyclopentadienyl compound. Moreover, they show markedly low olefin polymerization activities when a concentration of aluminoxane is low.
Under these circumstances, earnestly desired is a novel transition metal compound capable of being a catalyst component for olefin polymerization which shows high activities for olefin polymerization and produces an olefin polymer having excellent properties.